Automatic tracing device



Aug. 23, 1960 'r. E. DUGLE ETAL 2,949,739

AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 e Sheets-Sheet 1 aas ' l I l INVENTORS THOMAS E. DUGLE LOREN J. MEYERS BY DES JARDINS,ROBINSON & KEISER THEIR ATTORLLEXS 9 Sheets-Sheet 2 THEIR ATTORNEYS Aug.23, 1960 T. E. DUGLE ETAL AUTOMATIC TRACING DEVICE Original Filed July13, 1955 1960 T. E. DUGLE ETAL 2,949,739

AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9 Sheets-Sheet 3 IINVENTORS THOMAS E. DUGLE LOREN J. MEYERS BY DES JARDINS,ROBINSON &KEISER M MALL.

TH EIR ATTOR N EYS Aug. 23, 1960 T. E. DUGLE ETAL AUTOMATIC TRACINGDEVICE Original Filed July 13, 1955 9 Sheets-Sheet 4 IIO 27 IIO 235,-247 ,23s, 24a 226 INVENTORS THOMAS E. DUGLE LOREN J4 MEYERS BY DESJARDINS, ROBINSON 8. KEISER THEIR ATTORNEYS Aug. 23, 1960 T. E. DUGLE ETAL AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9 Sheets-Sheet5 l g l 567- IN V EN TORS THOMAS E. DUGLE LOREN J. MEYERS BY DESJARDINS, ROBINSON & KEISER THEIR ATTORNEYS Aug. 23, 1960 T. E. DUGLE ETAL AUTOMATIC TRACING DEVICE 9 Sheets-Sheet Original Filed July 15, 1955INVENTORS E. DUGLE MEYERS THOMAS LOREN J.

BY DES JARDINS, ROBINSON & KEISER THEIR ATTORNEYS g- 1960 T. E. DUGLE ETAL 2,949,739

AUTOMATIC TRACING DEVICE (D 2 mm JNVENTORS THOMAS E. DUGLE LOREN J.MEYERS BY DES JARD|N5,ROB|NSON 8. KEISER THEIR ATTOR NEYS T. E. DUGLEETAL AUTOMATIC TRACING DEVICE Original Filed July 13, 1955 9Sheets-Sheet 9 m m w V n v (D 0) v m in In v I!) ca v m (O v INVENTORSTHOMAS E. DUGLE LOREN J. MEYERS BY DES JARDINS, ROBINSON & KEISER THIggRATTORNEYS it tates AUTOMATIC 'I'RACING DEVICE Continuation of abandonedapplication Ser. No. 521,795, July 13, 1955. This application Sept. 11,1958, Ser. No. 761,277

8 Claims. (Cl. 60- 52) This application is a continuation of our patentapplication, Serial No. 521,795, for Automatic Tracing Device, filedJuly 13, 1955, now abandoned. The invention in this application, as inthe previous application, relates to a tracer control mechanism of thetype in which a finger or stylus is automatically caused to follow theoutline of a pattern through a full 360 degrees of movement of thefinger relative to the pattern. More specifically, the inventioncomprises an electric pickup type of tracer which is adapted to producean error signal whenever the tracer deviates from the pattern outline.This signal is then utilized to control the hydraulic actuators of themachine and return the tracer to the pattern outline. The tracer controlmechanism may be applied to any desired type of reproducing apparatuswhich is designed for hydraulic operation. For example, it may be usedto control the operation of an automatic profiling machine in which oneor more pieces of work are simultaneously contoured to conform to theoutline of a master templet or pattern. The form of apparatusconstituting the present invention provides certain advantages over theprior art forms of tracer mechanisms and has been designed with a viewto enabling rapid and eflicient reproduction of the master in theworkpieces. This is made possible by the use of electrical controlswhich provide rapid and accurate response to changes in direction of thepattern outline and to apply these controls to the electrohydraulicdevices which in turn control the hydraulic actuators of the machine.

in general, the present invention comprises a tracing finger which ismounted for rotation about its longitudinal axis so as to permit the useof eccentricity or anticipation in the system, and also for rotationabout a lateral axis so as to permit sidewise deflection of the fingerby the pattern. The sidewise deflection of the finger operates anelectrical pickup of the dilferential transformer type which produces anull signal when the tracer is following the pattern outline and anerror signal when the tracer departs therefrom. The phase of the errorsignal is indicative of the overdeflection and underdeflection of thefinger by the pattern. This signal is fed into a discriminator circuitand rectified so as to produce a direct current voltage whose polarityis dependent on the phase of the error signal. This voltage is thenamplified and utilized to control the engagement of a pair of magneticclutches which aiford a reversible drive to the gear which rotates thefinger about its longitudinal axis. This gear carries a sine-cosine camwhich adjusts the armatures of a pair of variable dilierentialtransformers which are spaced 90 degrees apart around the cam. Hence,the voltage produced by one transformer will vary as the sine of theangular displacement of the cam while the other voltage will vary as thecosine thereof. These voltages are amplified with care being taken tomaintain the linearity of the voltages throughout the various circuitsso as to preserve the sine-cosine relationship between the voltages. Theamplified voltages are then applied to the servo motors which in turnate control the displacement of a pair of variable displacement pumpswhich control the rate and direction of movement of the hydraulicallyoperated, transversely movable slides of the machine. Since the vectorsum of the sine and cosine components always remains the same regardlessof the position of the cam which turns with the tracing finger, andsince the response of the system to and including the variabledisplacement pumps is linear, the feed rate of the cutting tool of themachine, and also of the tracer, will remain the same in all directionsof travel. The correction applied by the error signal to the rotationalposition of the cam and finger is always such as to reduce the over orunderdeflection of the tracing finger thereby causing the tracer tofollow the direction of the pattern outline. Likewise, the rotationalposition of the finger and cam are always indicative of the direction oftravel of the cutting tool and tracing finger relative to the work andto the pattern.

Means is also provided for reducing the magnitude of the sine and cosinevoltages when the error signal exceeds a predetermined value so as toreduce the feed rate of the cutter when sudden changes in direction areencountered such as, for example, a right-angle corner on the pattern.This reduction of the magnitude of the sine and cosine voltages willreduce the error which would otherwise occur under such circumstancesdue to the inability of the machine to respond with sufficient rapidityto abrupt changes in direction of the pattern outline.

A variable speed drive is also provided for the variable displacementpumps so that the feed rate of the machine may be adjusted to suit therequirements of the work by simply increasing or decreasing the speed ofthe pumps. This is a decidedly advantageous feature inasmuch as iteliminates the low feed rate errors which normally are present inconventional forms of tracer mechanisms. It has been common practice inprior constructions to control the feed rate by varying the magnitude ofdisplacement of the sine-cosine cam or other displacement producingmeans, the magnitude being reduced when a reduced feed rate is desired.This reduction of magnitude, however, greatly increases the criticalnessof response of the devices controlled by the cam since the movement ofthese devices becomes very small in relation to the rotational movementof the cam. Hence, errors are introduced into the tracing system by theinability of the devices controlled by the cam to respond withsufiicient accuracy to small rotational movements of the cam to effectthe necessary control of the operating mechanism of the machine. With asystem employing variable displacement pumps, the same difficulty isencountered when an attempt is made to reduce the displacement of thepumps in order to achieve reduced feed rates. By so doing, the pumps areoperated around their positions of zero displacement so that theinherent mechanical errors become a greater proportion of the totaldisplacement and are, in effect, magnified and prevent accurateoperation of the tracing system at low feed rates. However, with thepresent system of reducing the speed of the pumps, these difficultiesare avoided and the system operates with the same accuracy at low feedrates as it does at high feed rates from the standpoint of the accuracyof the pickups, servos, and pumps. Hence, the criticalness of thecomponents of the system is avoided and the construction of the tracercontrol mechanism is simplified and rendered less costly than in thecase of previous forms of construction.

Accordingly, it is an object of the present invention to provide atracer control mechanism incorporating new and improved features ofconstruction and modes of operation.

Another object of the invention is to provide a novel means forcontrolling the feed rate of a hydraulically actuated machine tool.

Another object of the invention is to provide a new type of tracercontrol mechanism for machine tools which utilizes an electric tracinghead for producing electric signals to control a pair of variabledisplacement pumps which drive the hydraulic actuators of the machine.

Another object of the invention is to provide a novel means for causingthe feed rate of the cutting tool to be automatically reduced whensudden changes of direction in the pattern outline are encountered.

Another object of the invention is to provide a hydraulically operatedmachine tool in which variable displacement pumps are utilized forcontrolling the rate and direction of travel of the cutting tool andwhich in turn are controlled by electric signals produced by the tracinghead after being analyzed and amplified by control circuits which aredesigned to provide a linear response to the signals.

With these and other objects in view which will become apparent from thefollowing description, the invention includes certain novel features ofconstruction and combinations of parts the essential elements of whichare set forth in the appended claims and a preferred form or embodimentof which will hereinafter be described with reference to the drawingswhich accompany and form a part of this specification.

Referring to the drawings in which like reference numerals indicate likeor similar parts:

Fig. l is a front elevation of a milling machine to which is shownapplied the tracer mechanism constituting the present invention.

Fig. 2 is a diagrammatic view showing the manner in which the presentinvention is connected into the hydraulic system of the milling machine.

Fig. 3 is a cross-sectional elevation of the tracing head viewed fromthe front.

Fig. 4 is a perspective view of the eccentric adjustment for the tracingfinger.

Fig. 5 is a cross-sectional elevation of the tracing head taken alongthe line 5-5 in Fig. 6.

Fig. 6 is a horizontal cross-sectional view taken through the upper partof the tracing head.

Fig. 7 is a circuit diagram of a regulated power supply for delivering aconstant direct current voltage to the electrical control apparatus.

Fig. 8 is a circuit diagram of another regulated power supply fordelivering a constant direct current voltage to the electrical controlapparatus.

Fig. 9 is a circuit diagram of a control circuit for facilitating thechangeover from hand servo control to tracer control.

Fig. 10 is a circuit diagram of a portion of the electrical controlapparatus for the machine including the vacuum tube oscillator, and thethrottling circuit for effecting slow-down when a sharp corner isencountered.

Fig. 11 is a circuit diagram showing a portion of the rotation controlapparatus.

Fig. l2 is a circuit diagram of the electrical apparatus for controllingmovement of the table of the milling machine.

Fig. 13 is a circuit diagram of the electrical apparatus for controllingmovement of the cross-slide of the milling machine.

Fig. 14 is a block diagram of the tracing system.

Fig. 15 is a schematic view of the variable displacement pumps and thecontrolling apparatus therefor.

Machine tool In the accompanying drawings the invention forming thesubject matter of the present application is shown as applied to ahydraulically actuated milling machine of a known type. It is to berealized, of course, that the inventive features of the tracer controlapparatus could be used with equally satisfactory results with othertypes of hydraulically actuated machine tools where it is desirable toprovide means for reproducing in a workpiece the shape of a master orpattern. The milling machine shown in Fig. 1 comprises a bed 20' onwhich a work table 21 is mounted for longitudinal sliding movement.Supported on the bed behind the table is a cross-slide 23 which ismounted for horizontal sliding movement on ways 24 in a fore and aftdirection, that is, at right angles to the direction of movement of thetable 21. A tool head 25 carrying a power driven spindle 26 and cutter27 is mounted for vertical sliding movement on the cross-slide 23 so asto provide three dimensional movement of the cutter relative to aworkpiece 28 mounted on the table. On the right-hand side of the head 25is mounted a saddle 29 which is supported for horizontal slidingmovement in a fore and aft direction on the head by suitable ways 30.The saddle is provided with vertical ways on which a saddle 36 ismounted for vertical sliding movement. The saddle 36 is provided with ahorizontal arm 37 on which a tracing head slide 38 is mounted forhorizontal movement along the arm 37. A tracing head 39 is mounted onthe slide 38 so that a tracing finger 40 depending therefrom will movein unison with the cutter 27 and follow the contour of a pattern 41fastened to the table. Also, by virtue of the particular mounting of thetracing head 39 upon the tool head 25 just described, the tracing finger40 may be adjusted in any direction with respect to the cutter 27 forset up purposes.

The milling machine herein illustrated is of the same general type asthat shown in US. Patent No. 2,239,625, granted April 22, 1941, to ErwinG. Roehm and Hans Fritschi and, like the machine of that patent, isprovided with means for enabling hand operation of the table,cross-slide and head. For this purpose, a hand wheel 45 is mounted onthe front of the machine bed in a convenient position for manualoperation to effect traversing movement of the table 21 in one directionor the other depending upon the direction of rotation of the hand wheel.This movement of the table is effected hydraulically by a handservovalve, the plunger of which is moved in one direction or the otherin accordance with the direction of rotation of the hand wheel. Thevalve plunger is connected with the hand wheel 45 by means of suitablegearing and a half nut operating on a feed screw in the manner describedin the aforementioned patent. The cross-slide 23 may be caused to moveback and forth along the ways 24 in a similar manner by suitablemanipulation of a hand wheel 46 also mounted on the front of the machinebed 20. Likewise, vertical movement of the toolhead 25 may be effectedby manipulation of a hand wheel 47, or a hand wheel 48, which handwheels are geared together for a conjoint rotation. When the machine isunder control of the tracer, the hand servo controls are selectivelyrendered ineffective to prevent misoperation of the machine.

Hydraulic circuits The hydraulic actuators and the control apparatustherefor of the milling machine shown in Fig. l are illustrateddiagrammatically in Fig. 2 of the drawings. As therein shown, thehydraulic actuator of the table 21 comprises a hydraulic cylinder 55containing a piston 56 mounted on a piston rod 57 which is bolted to thetable. The table may be moved in either direction by selectivelycontrolling the flow of fluid to the opposite ends of the cylinder 55.The cross-slide 23 is operated by a similar hydraulic actuatorconsisting of a cylinder 58, piston 59 and piston rod 60 bolted to thecross-slide. In a like manner, the tool head 25 may be caused to move upor down on the cross-slide by means of a hydraulic cylinder 61 securedto the head and containing a piston Hydraulic fluid under pressure issupplied to the abovementioned actuators by means of a pump 65 driven bya motor 64 which draws the fluid out of a sump 66 and delivers it underpressure to a system of high pressure lines 67. Pressure in the lines 67is maintained constant under varying demands on the system by a pressurerelief valve 68 connected to the pressure side of pump 65 and having adischarge line 69 emptying into the sump 66.

The flow of high pressure fluid to the cylinders 55, 58 and 61 iscontrolled by hand servovalves 7t 71 and 72, respectively, when aselector valve 73 is set in the Hand position as shown in Fig. 2. Thevalve 73 includes a pair of valve plungers 74 and 75 which are connectedtogether for simultaneous operation by means of a centrally pivotedlever 76 to which the ends of the plungers are pivotally connected.Hence, when plunger 74 is moved to the left as viewed in Fig. 2 theplunger 75 will be moved to the right, and vice versa. With the selectorvalve 73 positioned as shown, the left-hand end of the cylinder 55 iscommunicatively connected with the right-hand motor port of valve 70 bylines 77 and 78. In a like manner, the right-hand end of the cylinder 55is communicatively connected with the left-hand motor port of valve 70by lines 79 and 80. The center, or pressure port of the valve 70 is, ofcourse, connected to the system of high pressure lines 67 while theexhaust ports of the valve are connected to a system of drain lines 81through which the hydraulic fluid is returned to the sump 66.

In a like manner, the hand servovalve 71 for the crossslide cylinder 58will be eflective to control the flow of fluid to and from itsassociated cylinder when the selector valve 73 is in the position shown.In this position of the valve, the left-hand end of cylinder 58 iscommunicatively connected with the right-hand motor port of valve 71 bylines 82 and 83. Likewise, the righthand end of the cylinder isconnected to the left-hand motor port by lines 84 and 85. The center, orpressure port of the valve is connected to the high pressure line 67 andthe exhaust ports are connected to the drain line 81.

The hand servovalve 72 is effective to control the flow of hydraulicfluid to and from the head cylinder 61 by means of line 86 whichconnects the upper end of the cylinder to the bottom motor port of thevalve and a line 87 which connects the lower end of the cylinder to thetop motor port of the valve. The center port of the valve is connectedto the high pressure line 67 and the exhaust ports thereof are connectedto the drain line 81.

From the foregoing it will be clear that when the machine is set forhand operation, each of the hand servovalves 76, 71 and 72 will berendered effective to control the flow of fluid under pressure to andfrom the cylinders of the hydraulic actuators. The direction of movementof the pistons within the cylinders will be dependent upon the directionof movement of the plungers of the valves which, in hand operation ofthe machine, is effected by hand wheels 45, 46, 47 and 48 (Fig. 1) whichare connected through gearing with half nuts moving with the valveplungers. This mechanism is fully described in the previously mentionedU.S. Patent No. 2,239,625 and need not be described in detail hereinexcept insofar as is necessary for an understanding of the manner inwhich the changeover is effected from hand servo control to tracercontrol.

Referring again to Fig. 2, the plunger of the hand servovalve 71 isbored to slidably receive a feed screw 90 which is bolted to the table21. As diagrammatically illustrated herein, the feed screw 99 is adaptedto be engaged by a half nut 91 which is carried by and moves with theplunger of the valve and is pivoted thereto for movement into or out ofengagement with the feed screw 90. As described in the aforementionedpatent, the

plunger and half nut may be rotated by means of a gear 92 connected tothe hand Wheel 45 for rotation thereby. Hence, with the half nut engagedwith the feed screw 90, rotation of the plunger and half nut will causethe plunger to be fed along the screw thereby admitting fluid underpressure to one end of the cylinder 55 and connecting the other end ofthe cylinder to drain. The resulting movement of the piston 56 willcause movement of the table 21 which in turn will center the plunger ofthe valve to stop further movement of the table, the body of the valvebeing fast on the bed of the machine. When the half nut is disengagedfrom the feed screw, however, the table will then be free to move withreference to the valve plunger as is necessary in operating the machineunder tracer control.

The hand servovalve 71 for the cross-slide cylinder 58 is constructedand arranged in the same manner as the valve 70 just described. That is,the plunger of the valve is bored to slidably receive a feed screw 95which is bolted to the cross-slide and adapted to be engaged by a halfnut 96 pivotally supported on the plunger of the valve. Rotation of theplunger and half nut may be effected by manipulation of the hand wheel46 (Fig. 1) which is connected by suitable gearing with a gear 97rotating with the plunger. Hence, the cross-slide may be moved back andforth under power by suitable manipulation of the hand wheel 46 which,when the half nut 96 is engaged, causes feeding movement of the plungerof the valve along the feed screw and produces corresponding movement ofthe cross-slide while the hand wheel is being turned.

The servovalve 72 for the head cylinder 61 is similarly constructed. Theplunger of this valve is bored to slidably receive a feed screw 100which is adapted to be engaged by a half nut 101 pivotally supported onthe valve plunger. Rotation of the plunger and half nut by the handwheels 47 and 48 (Fig. 1) is effected by a suitable drive from the handwheels to a gear 162 which rotates with the plunger of the valve.Therefore, with the half nut engaged, rotation of the hand wheels willcause feeding movement of the plunger along the feed screw and causecorresponding movement of the cylinder 61 relative to the cross-slide23. For reasons later to be explained, the plunger of the valve 72 isbiased upwardly by a spring 163 compressed between an offset in thevalve body and a flange formed on the valve plunger. So long as the halfnut 161 is engaged with the feed screw 100, however, the spring 103 isineffective to move the valve plunger out of its centered position.

Each of the half nuts 91, 96 and 161, is normally biased into engagementwith its related feed screw but may be disengaged therefrom upon theapplication of hydraulic pressure to a small hydraulic actuatorassociated with each half nut. As shown in Fig. 2, the hydraulicactuators for the half nuts 91 and 96 are connected by a line 105 with aport on the selector valve 73. This port is connected with the drainline 81 when the plunger 75 of the valve is in the position shown inFig. 2. Hence, when the selector valve is set for hand servo operation,the half nuts will be engaged with their related feed screws. When,however, the valve 73 is shifted to Tracer position, a port on theselector valve connected with high pressure line 67 will becommunicatively connected with the line 105 to thereby supply pressureto the actuators for the half nuts 91 and 96 and remove these half nutsfrom the feed screws 90 and 95. This will cause the valves 70 and 71 forthe table and cross-slide to be conditioned for a tracer operation bydisassociating the valve plungers from their associated feed screws soas to permit the feed screws to move within the plungers without anyinterference thereby during operation of the machine under the controlof the tracer.

The hydraulic actuator for the half nut 101 is con nected by a line 106with a port on a solenoid valve 107. In hand servo operation, this valveis normally energized, as shown in Fig. 2, to connect the line 106 Withthe drain line 81 connected to another port on the valve. Accordingly,the half nut 101 will be permitted to engage its feed screw 100 toenable hand operation of the tool head 25. When the machine is set fortracer control, the same condition prevails with respect to the handservovalve 72, i.e., the half nut 10L remains engaged with the feedscrew 100 under normal conditions of operation under tracer control.This permits raising and lowering of the tool head under control of handwheels 47 and 48 during tracer control in the same manner as when themachine is set for hand servo operation.

Tracing head When the machine heretofore described is to be used for theautomatic reproduction of a master or pattern, it is placed under thecontrol of the tracing head 39, the tracing finger 40 of which isadapted to contact the edge of the pattern 41 and to follow the outlineof the pattern as the tracing operation proceeds. As shown in Figs. 3,4, 5 and 6 of the drawings, the tracing head 39 is mounted in a casing110 which is in the form of a hollow box having removable top and sidepanels which afford access to the interior of the head. In the bottom ofthe casing there is provided a circular opening for receiving the upperend of a cylindrical housing 111 which is secured to the casing 110 byfastening screws 112. Rotatably journaled Within the housing 111 is asleeve 113 within which the stem 114 of the tracing finger 40 is housed.As shown in Fig. 3, the sleeve 113 is journaled for rotation within thehousing 111 by an upper set of ball bearings 117 and a lower set ofroller bearings 118. The ball bearings 117 are retained within a recessprovided in the upper end of the housing 111 by a retaining ring 119which is held in place on the upper end of the housing by suitablefastening screws. The roller bearings 118 are retained within a recessprovided in the lower end of the housing by a bottom cap 120 which isfastened to the bottom of the housing by screws 121. The sleeve 1 13 isprovided toward its lower end with a taper 122 which is adapted toengage a similar taper formed on the inner race of the roller bearing118, the taper 122 being seated therein and held thus engaged by a drawnut 123 meshing with a screw thread 124 provided on the sleeve justabove the taper 122. The interior of the housing 111 is sealed againstthe entrance of dust and dirt by a ring or gasket 125 of syntheticrubber or similar material which also serves as an oil seal between thelower end of the housing and the sleeve 113.

Near its lower end, the stem 114 is provided with a spherical prominence130 which seats in a counterbore formed in the lower end of a pivot ring131 which is securely fastened to the bottom of the sleeve 113 by a ball132 forced into a V-shaped groove in the sleeve by a set screw 133 inthe ring and a locating pin 134 in the ring which projects into a groove135 formed in the sleeve. The stem 114 is constrained to rotate with thesleeve 113 due to the engagement of the inner end of a pin 136-in thering engaging with a groove 137 formed in the ball pivot 130. Rotationof the sleeve and stem is effected by means of a spur gear 140 mountedupon and keyed to the upper end of the sleeve 113. If desired, a degreescale may be inscribed on the peripheral face 141 of the ring 131 sothat the angular position of the tracing finger with relation to thehousing 111 of the tracing head may be determined by reading the scaleagainst an index line inscribed on the peripheral face 142 of the cap128. Also, a portion of the face 141 is preferably knurled so as tofacilitate turning the ring 131 by hand for a purpose later to bedescribed.

Eccentricity of the lower end of the tracing finger 40 with respect tothe axis of rotation of the sleeve 113 is provided for by a coupler 145which serves to connect a cylindrical contact element 146 of the tracingfinger with a shank 147 formed on the bottom of the stem 114. Thecoupler 145 includes a top slide 148, a bottom slide 149 and a crossblock 150. The cross block is provided on its upper surface with afeather 151 which is slidable within a groove 152 formed in the upperslide 148. The block 150 is provided on its lower surface with a feather153 lying at right angles to the feather 151 and slidably receivedwithin a groove 154 in the bottom slide 149. The assembly is heldtogether by longitudinally extending screws 161.

The block 150 is provided with an upper pair of on positely disposedadjustment screws 155 adapted to bear against opposite sides of theshank 147 and also with a lower pair of adjustment screws 156 disposedat right angles to the screws and adapted to bear against opposite sidesof a dowel pin 157 mounted in the bottom slide 149. Also carried by theslide 149 is a pin 160 on the lower end of which the contact element 146is fastened. The pin is secured to the bottom slide 149 by a set screw158 and the upper slide 148 is secured to the shank 147 by a pin 159.Hence, by suitable adjustment of the screws 155 and 156, the contactelement 146 may be offset in any direction from the central axis of thestem 114 so that eccentricity may be introduced in any desireddirection.

As is well known in the art, it is desirable to offset the contactelement in the direction of tracing so as to provide a certain amount ofanticipation to compensate for the time lag in the response of thesystem to changes in direction of the pattern. Eccentricity of thecontact element with respect to its axis of rotation also introduces acertain amount of feed back into the system since it tends to reduce theerror signal in response to the ap plied correction. This, as is wellknown, tends to increase the stability of operation of the system.

Sidewise deflection of the element 146 by the edge of the pattern 41 istranslated into vertical movement of a plunger slidably mounted within abushing 166 inserted in the upper end of the sleeve 113 by means of :aball 167 which seats in conical recesses provided in the top and bottomof the stern 114 and plunger 165, respectively. The upper end of theplunger 165 bears against the bottom of a lever 168 which is pivoted at169 between a pair of brackets 170 secured to the bottom face of alaminated phenolic body 171 supported on the bottom of the casing 110 bythree posts 172. As shown in Fig. 3, the left-hand end of the lever 168lies beneath the lower end of a plunger 173 of a linear variabledifferential transformer 174 which includes a primary winding 175, apair of secondary windings 176 and a magnetic core 177 carried by theplunger 173 for axial movement relative to the primary and secondarywindings of the transformer. The plunger 173 is journaled for slidingmovement in upper and lower threaded plugs 178 and 179, respectively,which retain the windings of the transformer in position within the boreinto which the plugs are screwed. A compression spring 180 compressedbetween the bottom of a bore in the plug 179 and an abutment flange onthe plunger 173 urges the bottom end of the plunger into contact withthe top edge of the lever 168.

A predetermined amount of downward pressure may be applied to theplunger 165 by means of a spring pressed plunger which is slidablymounted within an ex ternally threaded sleeve 186 which screws into athreaded hole provided in the body 171. The plunger 185 is located inaxial alignment with the plunger 165 and is pressed downwardly by aspring 187 which is compressed between the top of the plunger 185 andthe lower end of a screw 188 which screws into the upper end of thesleeve 186. Screw 188 is provided with a knurled head 189 whereby thescrew may be turned to adjust the compressive force of the spring 187against the plunger 186 so 9 that a predetermined sidewise force must beapplied to the contact element 146 to produce deflection of the stem 114and elevation of the plunger 173 of the differential transformer 174.

As will be more fully explained hereinafter, the differentialtransformer .174 operates to produce an electric signal which mayappropriately be referred to as an error signal whenever the tracingfinger 40 departs from its position of normal deflection. The tracinghead 39 is provided with two additional linear variable differentialtransformers 195 and 196 (Fig, 6) which will hereinafter be referred toas the sine and cosine transformers or pickups since they are soarranged as to produce a pair of AC. voltages whose amplitudes vary asthe sine and cosine functions of the rotational position of the tracingfinger 40, and whose phase shift is determined by the algebraic sign ofthe sine-cosine functions. As will be observed from Fig. 6, the lastmentioned transformers are so mounted in the body 171 as to lie 90degrees apart about the central axis of the rotatable sleeve 113. Thetransformers 195 and 196 are provided with plungers 197 and 198,respectively, which hear at their lower ends against a sine-cosine cam199 (Fig. formed on the upper face of the gear 140. The cam 199 is soshaped as to provide a vertical displacement of the plungers 197 and 198which varies as the sine and cosine functions of the angular position ofthe gear 140.

Inasmuch as the transformers 195 and 196 are of identical construction,it will be necessary to show and describe only one of them for acomplete understanding of the invention. As shown in Fig. 5, thetransformer 195 includes a primary winding 205 and a pair of secondarywindings 266 which windings are of cylindrical form and are receivedwithin a bore within which they are retained by upper and lower threadedplugs 267 and 298, respectively. The plugs are centrally apertured toreceive the plunger 197 and serve to guide the plunger for axialmovement relative to the windings. The plung er carries a magnetic core209 which may be moved by the plunger in one direction or another from acentered or null position. A light compression spring 2113 surrounds thelower end of the plunger 197 and urges the plunger downwardly againstthe face of the cam 199. The purpose and mode of operation of thesine-cosine transformers will be described in a later portion of thespecification.

The rotational position of the tracing finger 4% is effected through thegear 140 by means of a pair of magnetic clutches 215 and 216 (Fig. 5)which are located within the casing 110 of the tracing head. Power isprovided for driving the clutches by an electric motor 222 supported onthe plate 38 (Fig. l) which drives a shaft 223 through suitablereduction gearing 224- and a drive coupling 225. The shaft 223 issupported for rotation within a cylindrical housing 226, mounted on onecorner of the casing 110', by means of upper and lower ball bearings 227and 228 which are retained and enclosed by upper and lower bearing caps229 and 230, respectively. The shaft carries inion gear which is pinnedor otherwise keyed to the shaft and which drives a pair of meshing spurgears 235 and 236 journaled for rotation on shafts 217 and 218,respectively, which in turn are journaled for rotation in the casing 116by ball bearings 221.

As shown by the cross-sectional representation of the clutch 216, eachof the magnetic clutches includes a floating armature disc 237, a rotor238 and a stationary field coil 239. The floating armature disc 237 isconstrained to rotate with the driving gear 236 while being free to movethrough a limited distance axially of the gear. The rotor 238 is rigidlysecured to the shaft 218 and forms a part of the magnetic circuitcreated by the stationary field coil 239 when the latter is energized.The field coil 239 is enclosed in a housing 242 which is journaled by abushing 241 on a sleeve 240 formed integrally with the rotor 238. Themagnetic clutches 215 and 216 are of a conimercially available type andthe detailed features of construction thereof are not important insofaras the present invention is concerned.

Engagement of each of the clutches is effected by energization of itsfield coil 239 which sets upa magnetic flux through the rotor andarmature disc of the clutch which attracts the armature disc to therotor and causes the mating faces 243 thereof to be frictionally engagedthereby causing the rotor to be driven by the driving gear. Keyed to theshafts 217 and 218 are spur gears 247 and 248 each of which meshes withthe spur gear (Fig. 6). Since the driving gears 235 and 236 are rotatedin opposite directions, the gear 146' will be driven in one direction orthe other depending upon which of the clutches 215 or 216 is energizedto the greater degree as determined by the phase of the error signalproduced by the differential transformer 174. The operation of theclutches under the control of this transformer will be fully describedin a later portion of this specification.

DC. power supplies The electronic control equipment for the tracer whichis shown in Figs. 10, 11, 12 and 13, and which is housed in anelectrical cabinet 256 (Fig. 1), requires a source of constant DC.voltage in order to insure linear amplification and handling of thesignals supplied thereto by the differential transformers in the tracinghead. For this purpose, the regulated power supplies shown in Figs. 7and 8 of the drawings are provided. The supply shown in Fig. 7 providesapproximately 300 volts DC. at the plate voltage supply terminal 255while the supply shown in Fig. 8 is intended to provide a source ofapproximately 400 volts DC. at the terminal 256 for the direct currentamplifier circuits of the control apparatus.

The power supply shown in Fig. 7 includes a power transformer 257 havinga primary winding adapted to be connected by terminals 253 to the powerline, and a center-tapped secondary Winding for operating the plates ofa full-wave rectifier tube 258. In order to provide a delay to allow thefilaments of the vacuum tubes of the electronic circuits to heat upbefore plate voltage is applied thereto, a thermostatic type delay relay259 has its heater connected in parallel with the primary winding of thetransformer so as to cause the normally open contacts 254 of the relayto close at a predetermined time after energization of the primarywinding of the transformer. Contacts 254 control the energization of arelay coil 260, the forward contacts 261 of which are inserted in theline connecting the center tap of the secondary winding to grotmd.Therefore, voltage cannot be supplied by the transformer and rectifiertube to the terminal 255 until the contacts 254 are closed after apredetermined time delay.

The rectified AC. voltage furnished by the tube 258 is filtered by choke262, condenser 263 and load resistor 264. The output from the filter isapplied to the output terminal 255 through a regulator tube 265 which isof a low mu, twin triode designed intended for DC. amplifier service.The two sections of the tube are connected in parallel to increase thecurrent handling capacity of the tube. The grid bias of the tube 265 isdetermined by the voltage on the plate of a twin triode control tube266. The voltage on the cathode of the left-hand section of the tube isstabilized by a voltage regulator tube 267 while the voltage on the gridof this section is determined by the voltage on the plate of theright-hand section of the tube. The cathode of the right-hand section isconnected to a tap on a voltage divider connected in series between theoutput terminal 255 and ground, and the voltage on the grid of thissection of the tube is maintained constant inasmuch as it is suppliedfrom a tap on a voltage divider connected across the voltage regulator267. Hence, any change in voltage at the output terminal 255 will resultin a change of voltage on the cathode of the right-hand section oftube'266 thereby changing the bias on this section of the tube andvarying the plate voltage which changes the bias on the left-handsection of the tube. This varies the voltage on the left-hand platethereby adjusting the bias on the regulator tube 265 so as to increaseor decrease the voltage drop across this tube and thereby restore thepotential on the output terminal to the correct value.

The voltage regulator shown in Fig. 8 is of a similar character andincludes a power transformer 270 having a center-tapped secondarywinding which supplies AC. voltage to the plates of three full-waverectifier tubes 271. The heater of a thermostatic type delay relay 272is connected in parallel with the primary winding of the transformer andcontrols the energization of a relay coil 273 which, when energized,closes relay contacts 274 connected between the center tap of thesecondary winding and ground. Therefore, no voltage will be supplied tothe terminal 256 until the coil 273 is energized after a predeterminedinterval following energizat-ion of the primary winding of thetransformer.

The rectified output from the tubes 271 is filtered by choke 275,condensers 276 and resistor 277 and the filtered output is supplied tooutput terminal 256 through a plurality of parallel-connected regulatortubes 278. The voltage drop across tubes 278 is controlled by twintriode tube 279 in which the voltage on the cathode of the left handsection and on the grid of the right-hand section are stabilized by thevoltage regulator tube 280. The voltage regulator circuit includingtubes 278, 279 and 280 operates in the same manner as the voltageregulator shown and described in Fig. 7 to control the voltage at theoutput terminal 256 and to maintain it constant under varying conditionsof load.

Alternating current generator To eliminate stray pickup and to providefast response by the rotation control system of the tracer, thedifferential transformers 174, 195 and 196 (Fig. 6) of the tracing headare supplied with an energizing voltage of approximately 10,000 cyclesper second provided by a local A.C. voltage generator. This generator,which, in the present embodiment, comprises a vacuum tube oscillator ofthe Wein-bridge type, is illustrated in the upper lefthand corner ofFig. of the drawings. The oscillator includes a twin triode type vacuumtube 285 the output from the left-hand section of which is inverted andamplified by the right-hand section of the tube. The output of theright-hand section is fed back to the input of the left-hand section ofthe tube through a coupling condenser 286. The feedback voltage ispassed through a frequency discriminating network including series-comnected condenser 287 and resistor 288, and parallel-connected resistor289 and condenser 290. The values of these components are so chosen asto favor a frequency of 10,000 cycles per second and thereby cause thecircuit to oscillate at that frequency. A degenerative feedback voltageis applied to the left-hand section of the tube 285 by a voltage dividerconsisting of the filament of a lamp 291, a resistor 292 and a variableresistor 293. The amount of negative feedback may be controlled bymanipulation of the resistor 293 so as to maintain the amplitude ofoutput from the left-hand section of the tube at a low enough level toinsure that the wave form will be approximately sinusoidal. The 300 voltpower supply of Fig. 7 provides a constant voltage source for operatingthe oscillator, the plates of the tube 285 being connected to the outputterminal 255 of this power supply.

The 10,000 cycle voltage from the oscillator is taken from the cathodeof the right-hand section of tube 285 and applied through a line 295 tothe grid of the lefthand section of a twin triode vacuum tube 296 theplates of which are supplied from the supply terminal 255. The left-handsection of the tube 296 is connected in a cathode follower arrangementwith the input of the righthand section through a band pass filter toimprove the wave form of the 10,000 cycle voltage. This filter includesseries connected resistors 297 and capacitors 298, and parallelconnected resistors 299 and capacitors 300 together with parallelconnected inductances 301. The filter is designed to discriminateagainst frequencies above and below 10,000 cycles per second so as tofurnish a pure 10,000 cycle signal to the grid of the right-hand sectionof tube 296. The right-hand sect-ion of the tube operates as a phaseinverter, the signal being taken from the cathode and plate thereof anddelivered through lines 303 and 304 and coupling condensers 305 and 306to the grids of a push-pull amplifier tube 302.

Rotation control circuit The plates of the tube 302 are supplied fromthe regulated voltage supply of Fig. 7 through a load resistor 308 andthe center tap of a primary winding of the transformer 307. Thesecondary winding of the transformer is connected in series with theprimary winding of the differential transformer or pickup 174 (Fig. 3)so as to energize this winding with 10,000 cycle voltage. As shown inFig. 10, the secondary windings 176 of the transformer 174 are connectedin phase opposition between ground and an output lead 309 which isconnected through a coupling condenser 310 to the grid of an amplifiertube 311. If desired, the connection between secondary windings 176 maybe connected to the slider of a potentiometer 312 connected across theouter ends of the windings so as to enable the balance point voltage ofthe transformer to be adjusted to a minimum value in a known manner.

When the tracing finger 40 is deflected sufliciently from the verticalposition as shown in Fig. 3 to rock the lever 168 about its pivot 169and elevate the core 177 of the transformer to its centered or nullposition, a zero signal will be delivered to the grid of tube 311.However, if the tracing finger 40 is underdeflected or overdeflected, a10,000 cycle signal will be delivered to the tube through the outputlead 309 due to the unbalance of the bucking voltages in the secondarywindings 176. The phase of the error signal voltage will shift through180 degrees at the null or balance point of the transformer due to thephase opposition of the voltages induced in the secondary windings 176.Hence the error signal produced -by an overdeflection of the tracingfinger will be 180 degrees out of phase with the error signal producedby an underdefiection of the finger. Also, the amplitude of the errorsignal will, by virtue of the linear characteristic of the transformer174, be directly proportional to the extent of displacement of thefinger from its position of normal displacement.

The l0,000 cycle error signal delivered to the grid of the tube 311 fromthe transformer 174 is amplified and delivered through a potentiometer316 to a line 317 which is connected to the grid of a phase invertertube 315 (Fig. 1 1). The plate and cathode of the tube 315 are connectedthrough condensers 318 and 319, respectively, with the grids of a twintriode vacuum tube 320 whose plates are fed from the supply terminal 255through the center-tapped primary winding of a transformer 321. The tube320 is connected in a conventional push-pull arrangement and theamplified 10,000 cycle error signal appearing in the plate circuit ofthe tube is fed into a discriminator circuit which includes the centertapped secondary winding of the transformer 321 and a pair of seriesconnected potentiometers 322 and 323 whose sliders are ganged forconjoint movement as indicated by dotted line 324. The potentiometersprovide a sensitivity control, the sliders moving in unison toward thepoint of connection between the two potentiometer windings for thepurpose of decreasing sensitivity, and toward the outer or high ends ofthe windings for increased sensitivity.

The phase of the error signal fed to the discriminator by the vacuumtube 320 is compared with the phase of the amplified signal from theWien-bridge oscillator appearing on the bottom plate of the tube 302('Fig. 10) which is fed through a line 325 into the center tap of thesecondary winding of transformer 321 by a small coupling condenser 326and a pair of voltage dividing resistors 327 and 328 connected betweenthe condenser and ground which adjust the amplitude and phase of thereference voltage with respect to the phase and maximum amplitude of theerror signal. The sliders of potentiometers 322 and 323 are directlycoupled to the grids of a twin triode vacuum tube 330 in which bias isprovided by a cathode biasing resistor and in which the plates aresupplied with a source of positive voltage provided by the terminal 255through suitable load resistors. Consequently, the voltage applied toone of the grids of the tube 330 will be the sum of the error signalvoltage and the reference voltage from the signal generator while thevoltage appearing on the other grid of the tube will be the differenceof these voltages so that the two halves of the tube will conductunequally when an error signal is present. Of course, if thedifferential transformer 174 is in its null position, the voltages onthe grids of tube 330 will be equal so that both sections of the tubeconduct equally.

The plates of tube 338 are connected by coupling condensers 331 and 332to the plates of a twin diode tube 333 where the voltages from the twosections of the tube 330 are rectified and passed directly to the gridsof a twin triode D.C. amplifier tube 334. The tube 334 is provided witha cathode biasing resistor 335 of substantial value and the grids of thetube are provided with a positive bias by a voltage divider comprised ofresistors 336 and 337 connected in series between supply terminal 255and ground, the grids being connected to the junction between theresistors through suitable grid resistors 338.

The plates of tube 334 are connected to the grids of a pair of DC. poweramplifier tubes 351 and 352 through a derivative damping networkcomprised of resistors 346, 347 and 348 and condensers 349 and 359. Theplates of the tubes 351 and 352 are connected with the supply terminal256 (Fig. 8) through a reversing switch 355, the energizing coils 239(Fig. of the clutches 215 and 216, normally open relay contacts 358-1controlled by a relay 358 (Fig. 9), and a resistor 359. A source ofstabilized DC. voltages is provided for the screen grids of tubes 351and 352 by means of a pair of series connected voltage regulator tubes362 and 363, and the bias on tubes 351 and 352 may be adjusted by meansof a rheostat 366 connected in series with a cathode biasing resistor367 which is common to both tubes. When the machine is conditioned forhand servo control, the plates of tube 334 and the grids of tubes 351and 352 are grounded by two pairs of normally closed contacts 358-2 and358-3 cont-rolled by the relay 358 (Fig. 9).

The derivative damping network comprised of resistors 346, 347 and 348,and condensers 349 and 350, operates as follows: When the tracing finger40 is in its null position, both sections of twin triode tube 334 willconduct equally so that the voltages on the plates will be equal, theload resistors in the two plate circuits being of equal value. If now,the tracing finger undergoes a large deflection due to an abrupt changein the pattern outline, a potential difference will suddenly appearbetween the plates of the tube 334, one plate becoming more positivewhile the other plate becomes more negative. Which plate becomes morepositive and which more negative depends, of course, on whether thetracing finger is overdefiected or underdefieeted. The machine beingunder tracer control, the contacts 358-2 and 358-3 are now open and theresistors 346, 347 and 348 are efiectively in series between the platesof tube 334 with the grids of tubes 351 and 352 connected across theresistor 347. The sudden voltage impulse developed between 14 the platesof tube 334 will appear instantaneously across the resistor 347 due tothe inability of condensers 349 and 350 to charge instantaneously. Thiswill cause a large difference in potential to appear between the gridsof tubes 351 and 352 and a correspondingly large difference in theamount of current flowing through the coils 239 of the clutches. Hence,a large torque will be applied by the clutches to the gear to acceleratethe tracing finger rapidly in whichever direction is necessary to reducethe deflection of the finger caused by the pattern. The condensers 349and 350 will then charge and cause a voltage drop to occur acrossresistors 346 and 348 and reduce the voltage drop across resistor 347and the voltage between the grids of tubes 351 and 352. This reduces theditference in current flow between the coils 239 and causes acorresponding reduction in the torque on gear 140'. After a suflicientperiod of time, depending upon the time constant of the chargingcircuits of the condensers 349 and 350, the voltage between the plateswill divide normally among the three resistors and the torque on gear140 will become constant. It will be appreciated, of course, that whenzero error signal is present, the tubes 351 and 352 will conduct equallyso that the magnetic clutches 215 and 216 (Fig. 5) will be in balanceand no rotation of gear 140 will occur.

The purpose of contacts 358-1 (Fig. 11) is to break the plate circuit oftubes 351 and 352 when the relay 358 (Fig. 9) is de-einergized and.thereby deactivate the clutches 215 and 216 so that the ring 131 (Fig.3) can be turned by hand. At the same time, the contacts 358-2 and 358-3will be closed thereby grounding the grids of tubes 351 and 352 so as toprevent excessive screen current from flowing through the tubes whilethe plates are cut off.

The control apparatus just described for effecting rotation of thetracing finger in response to an error signal created by overdeflectionor underdefiection of the finger may appropriately be referred to as therotation control since it functions to maintain the direction ofeccentricity of the tracing finger tangent to the conotur of thepattern. By means which will now be described, the relative movement ofthe table and cross-slide is controlled by the angular position of thetracing finger so as to cause the finger to move relative to thepattern, and the cutter to move relative to the workpiece, in thedirection of the eccentricity of the tracing finger. The basic directionof tracing may be reversed by operating the reversing switch 355 mountedon the front of the head 39 (Fig. 1), which reverses the direction ofcorrection applied to the tracing finger by the magnetic clutches.

Table control circuit As was mentioned earlier in the description, apair of sine-cosine transformers or pickups 1 95 and 196 is arranged inthe tracing head 39 for co-operation with the contour of a sine-cosinecam 199 fashioned on the upper face of the gear 140. The transformer orpickup 196 controls the movements of the table 21 of the machine whilethe transformer or pickup controls the movement of the cross-slide 23.

Referring to Fig. 10; a potentiometer 375 is connected in the cathodecircuit of the right-hand section of tube 296. The slider of thispptentiomelter is connected through a condenser 376 with the grid of athrottle tube 377. The arrangement and functioning of this tube in thecircuit will be fully described at a later point in this specificationand for the present it will be sufiicient to state that the plate of thetube is connected by a con denser 378 to ground through a potentiometer379 whose slider is connected with the grid of a phase inverter tube380. The plate and cathode of this tube are connected through couplingcondensers with the grids of a push-pull amplifier tube 381 whose platesare fed from the supply terminal 255 through a dropping resistor and acenter tap on the primary winding of a transformer 15 382. Hence, the10,000 cycle voltage generated by the Wien-bridge oscillator will bedelivered to the secondary winding of transformer 382 one end of whichis connected to ground and the other end of which is connected by a line383 (Fig. 12) to one end of the primary Winding 384 of the diflerentialtransformer 196. The other end of the primary winding is connected toground so that a 10,000 cycle energizing voltage will be supplied to heprimary winding of the transformer. The transformer 196 is provided witha magnetic core 385 and with a pair of secondary windings 386 connectedin phase opposition in the same manner as the cross-slide transformer195 (Fig. One end of the combined secondary windings 386 is connected toground while the other end is connected to ground through apotentiometer 388. The slider of potentiometer 388 is connected to thegrid of a phase inverter tube 389 the plate and cathode of which areconnected to the grids of a push-pull amplifier tube 390 throughsuitable coupling condensers. The plates of the tube 390 are fed fromthe supply terminal 255 through a center tap on the primary winding of atransformer 391. The center tapped secondary winding of the transformer391 is connected in push-pull with the grids of a discriminator tube 392whose plates are tied directly to the supply terminal 255. The phase ofthe 10,000 cycle voltage delivered by the differential transformer 196and appearing in the secondary winding of transformer 391 is comparedwith the phase of a reference voltage of the same frequency in the inputcircuit of discriminator tube 392. This reference voltage is derivedfrom a line 393 connected to one plate of amplifier tube 381 (Fig. andis applied to the center tap of the secondary winding of transformer 391(Fig. 12) by a coupling condenser 394 which, together with a resistor399, suitably adjust the amplitude and phase of the reference voltagewith respect to the maximum amplitude and phase of the control voltage.The grid and cathode of each section of tube 392 is operated well aboveground potential by means of a pair of resistors 395 and 396 which areof considerably greater ohmic resistance than the biasing resistors 397and 398 of the tube. Discriminator tube 392 operates in essentially thesame manner as the previously described discriminator 330 (Fig. 11) tocause one section of the tube 392 to conduct more heavily than the otherdepending on the phase of the voltage delivered to the transformer 391by the differential transformer 196. If the magnetic core 395 of thetransformer is in its centered or null position, no signal will bedelivered thereby to the transformer 391 and the two sections of tube392 will conduct equally.

The cathodes of tube 392 are coupled by condensers to the plates of arectifier tube 402 the cathodes of which are coupled directly to thegrids of a DC. pushpull amplifier tube 403. The grids and cathodes ofthe tube 403 are balanced to ground by suitable resistors and a sourceof A.C. dither voltage 404 is introduced onto the cathodes of the tubeby a transformer 405 whose primary winding is connected to the source404 and whose secondary winding is connected to the cathodes of thetube. The frequency of the voltage source 404 may be as desired and inthe case of the present apparatus is derived from a 110 volt, 60 cyclesource.

The plates of the D.C. amplifier tube 403 are fed from the supplyterminal 256 through a balancing potentiometer 408 and a pair ofsuitable load resistors. The output of tube '403 is fed to a DC. poweramplifier 486. For this purpose, the plates of tube 40-3 are directlycoupled to the grids of DC. power amplifier tubes 409 and 410 and alsoto the grids of parallel connected tubes 411 and 412, which are of thesame type as tubes 409 and 410. The plates of the power amplifier tubesare fed directly from the regulated voltage supply terminal 256 whilethe screen grids of the tubes are connected to the supply throughsuitable voltage dropping resistors.

connected power amplifier tubes 442 and 443.

The cathodes of the tubes are connected to ground through biasingresistors 413 and 414 and are adapted to provide energizing current fora solenoid 415 one end of which is connected to the cathodes of tubes409 and 411 and the other end of which is connected to the cathodes oftubes 410 and 412 as shown in Fig. 12. Consequently, when the outputvoltage from the differential transformer 196 is zero, equal currentswill flow through the two pairs of tubes 409, 411 and 410, 412 and zerocurrent will flow through the coil 415 since the resistances of 413 and414 are equal. However, when a signal is supplied to the circuit fromtransformer 196, a current will flow through coil 415 in one directionor the other depending on the direction of displacement of the core 385of the transformer from its centered or null position.

Cross-slide control circuit The cross-slide 23 of the machine shown inFig. 1 is controlled by a circuit which is similar to the circuit justdescribed in connection with the table 21. As shown in Fig. 10, theplate of throttle tube 377 is connected by a line 420 with the grid of aphase inverter tube 421 the plate and cathode of which are connected tothe grids of a push-pull amplifier tube 422 bysuitable couplingcondensers. The plates of the tube 422 are fed from the supply terminal255 through a dropping resistor and a center tap on the primary windingof a transformer 423. The secondary winding of the transformer has oneend connected to ground and the other end connected to a line 424 which,as shown in Fig. 13, is connected to one end of the primary winding 205of differential transformer 195, the other end of which winding isconnected to ground. The primary winding of the transformer is therebysupplied with a source of 10,000 cycle energizing voltage from theWien-bridge oscillator. The secondary windings 206 of the transformerare as hereinbefore stated connected in phase opposition between groundand an output line 425 which is connected to ground through apotentiometer winding 426. The slider of the potentiometer is connectedto the grid of a phase inverter tube 427 the plate and cathode of whichare connected by coupling condensers with the grids of a push-pullamplifier tube 428. The plates of the tube 428 are fed from the supplyterminal 255 through the center tap of a primary winding of atransformer 429 having a secondary winding the ends of which areconnected to the grids of a discriminator tube 430. A 10,000 cyclereference voltage is delivered to the center tap of the secondarywinding of transformer 429 through a coupling condenser 431 and a line432 (Fig. 10) which is connected to one of the plates of the amplifiertube 422. The discriminator tube 430 is. arranged and functions in thesame manner as the discriminator tube 392 (Fig. 12) of the table controlcircuit so as to cause one section of the tube to conduct a largersignal than the other section depending on the phase of the voltagedelivered to the transformer 429 by the differential transformer 195.

The plates of the tube 430 are connected through coupling condensers tothe plates of a rectifier tube 435 the cathodes of which are connecteddirectly to the grids of a DC. push-pull amplifier tube 436. The gridsand cathodes of the tube 436 are balanced to ground through suitableresistors provided for this purpose and a source of A.C. dither voltage437 is applied to the cathode of the tube through a coupling transformer438. The plates of the tube 436 are fed from the supply terminal 256through a balancing potentiometer 439 and suitable load resistors. Theoutput of tube 436 is fed to a DC. power amplifier 434, the plates ofthe tube 436 being directly coupled to the grids of DC. power amplifiertubes 440 and 441 and to the grids of parallel The plates of the poweramplifier tubes are connected directly to the supply terminal 256 whilethe cathodes thereof are connected to ground through biasing resistors444 and 445 of equal value. The power amplifier tubes serve to energizea solenoid 446 one end of which is connected to the cathodes of thetubes 440 and 442 and the other end of which is connected to the cathodeof tubes 441 and 443.

'As in the case of the table control circuit, when the magnetic core 289of the diflerential transformer 195 is in its centered or null position,a zero signal will be delivered to the circuit and the solenoid 446 willremain unenergized. When, however, a voltage is produced in the outputline 425 of the differential transformer, a current will flow throughthe coil 446 in one direction or the other depending on the phase of thevoltage delivered by the transformer 195.

It will be noted that inasmuch as the differential transformers 195 and196 each have a linear characteristic, and since the table controlcircuit and the cross-slide control circuit each is designed to preservethe linear relation of the output voltage from its related transformerall the way through to the solenoids 415 (Fig. 12) or 446 (Fig. 13), theamount of current flowing through each of these coils will beproportional to the extent of displacement of the magnetic core of itsassociated differential transformer thereby maintaining a sine-cosinerelation between the currents in the solenoids in response to thesine-cosine relationship between the displacements of the magnetic coresof the diflerential transformers 195 and 196.

Hydraulic tracer control As indicated diagrammatically in Fig. 2 and asshown in greater detail in Fig. 15, the solenoids 415 and 446 controlthe operation of servo motors 451 and 452, respectively, which in turncontrol the displacement of variable displacement pumps 453 and 454,respectively. Consideiing first the mechanism for controlling themovement of the table 21, it will be observed that a polarized armature455 associated with solenoid 415 is connected to the upper end ofplunger 456 of servovalve 457. This valve is mounted on a subframe 458which is preferably secured to the main frame of the machine tool. Theplunger 456 works in a follow up sleeve 459 which in turn is slidablewithin the valve body and is ported to cooperate with the lands on theplunger 456 to valve the hydraulic fluid to and from a power cylinder460. The cylinder contains a piston 461 mounted on the end of a pistonrod 462 which is pivotally connected to the yoke 463 of the variabledisplacement pump 453 for the table. The follow up sleeve 459 isconnected by a link 464 to an arm 465 fulcrumed at 466 on the frame 458.At its opposite end, the arm 465 is slotted to receive a headed pin 467mounted on the piston rod 462.

Referring to Fig. 2 of the drawings, a source of fluid under pressure isprovided for actuating the power cylinder 460 by a reducing valve 470which receives high pressure fluid from the high pressure line 67 andsupplies it at reduced pressure to a supply line 471 which is connectedto the center port of valve 457 (Fig. 15). The drain ports of the valveare connected to the drain line 81 of the system and the motor ports areconnected by lines 472 and 473 to the ends of cylinder 460.

When the solenoid 415 is energized by a flow of current therethrough inone direction, the plunger 455 will be raised thereby raising theplunger 456 of the servovalve to cause fluid under pressure to flowthrough line 473 into the lower end of cylinder 468 and raise the pistonand rotate the pump control arm 463 clockwise. Upward movement of thepiston rod 462 will raise the follow up sleeve 459 thereby centering thevalve plunger with respect to the sleeve and cutting off the flow of oilthrough the line 473. Conversely, when the current flow through thesolenoid 415 is in the opposite direction, the plunger 455 will bedepressed thereby lowering the valve plunger thus causing fluid underpressure .to be delivered "18 to the'upper end of the cylinder 466through line 472. This will move the piston downward and rock the yoke463 counterclockwise and lower the follow up sleeve 459 to cut off theflow of oil to the cylinder and prevent further movement of the pistonuntil further movement of the valve plunger in either direction iseffected whereupon the piston 461 will again follow the valve plunger inits movements. Hence, there is provided a servo mechanism for operatingthe yoke 463 of the variable displacement pump 453 in accordance withthe flow of current through the solenoid 415. In order to maintain thelinearity of the system, the solenoid must also have a linear responseso that movement of the valve plunger will at all times be proportionalto the amount of current flowing through the coil 415.

The servo motor 452 for the cross-slide pump 454 is similar to the servomotor 451 and includes a polarized solenoid plunger 475, a valve plunger476, a servovalve 477, a follow up sleeve 478, a power cylinder 479, apiston 480 Working in the cylinder and operating a piston rod 481connected to the yoke 482 of the variable displacement pump 454 for thecross-slide, a link 483 con-' nected to an arm 484 fulcrumed at 485 andconnected to the piston rod 481 by headed stud 486. Pressure fluid issupplied to the center port of the valve 477 through pressure line 471and the end ports of the valve are connected to the drain line 81 of thesystem. The motor ports of the valve are connected by lines 487 and 488to the upper and lower ends, respectively, of the cylinder 479. Theservo mechanism for the cross-slide operates in the same manner as thatfor the table to adjust the yoke 482 for the cross-slide pump 454 inaccordance with the amount of current flowing through the solenoid 446and in a direction corresponding to the direction of flow of currentthrough the coil.

The variable displacement pump 453 for operating the table 21 of themachine tool operates as a closed system with the hydraulic cylinder 55(Fig. 2) which, as heretofore explained, actuates the table 21. Thefluid delivery lines 495 and 496 of the pump are connected to ports onselector valve 73 which, when this valve is set for tracer operation,are connected to motor lines 77 and 79 while the servovalve lines 78 and80 will be disconnected from the cylinder so as to render the handservovalve 70 ineffective.

In a similar manner, the variable displacement pump 454 for thecross-slide is connected by delivery lines 497 and 498 with additionalports on the selector valve 73 so as to cause this pump to be connectedto the cylinder 58 for the cross-slide through lines 82 and 84 when thevalve is set for tracer operation. At the same time, the lines 83 and 85from the hand servovalve 71 will be disconnected from the cylinder so asto disable the valve and prevent hand operation of the cross-slide.

The system is protected against overloads by a relief valve 500 andcheck valves 501, 502, 583 and 504 in the case of the pump 453, and apressure relief valve 505 and check valves 506, 507, 508 and 509 in thecase of the pump 454. In the arrangement shown, these valves willby-pass fluid from one side of the pump to the other if the pressure inthe delivery lines exceeds the pressure setting of the relief valve.

Provision is made for replenishing any fluid loss from each of the pumpand cylinder systems due to leakage so that positive actuation of thetable and cross-slide will be assured. For this purpose, the pressuresupply line 471 is connected through opposed check valves 512 and 513with the delivery lines 495 and 496, respectively, and by similarlyarranged check valves 514 and 515 with the delivery lines 497 and 498.Hence, make-up oil will be delivered from the pressure line 471 to thelow pressure side of the pumps in whatever quantity is needed tomaintain the system filled with fluid. At the same time, the checkvalves will operate to prevent fluid from the high pressure side of thepump from entering the pressure line 471.

.1 The pumps 453' and 454 are arranged to be driven at varying speeds bypower supplied by an electric motor 520 (Fig. 15) which drives the inputshaft 521 of a variable speed drive 522 which may be adjusted byhandwheel 519. This drive may be of any desired type which will providea suitable range of speed variation between the input shaft 521 and anoutput shaft 523 which drives shafts 524 and 525 of the pumps 453 and454-, respectively, through gears 526 and 527 mounted on the pump shaftsand meshing with a gear 528 secured to the output shaft 523. By thismeans the feed rate of the cutter relative to the workpiece and of thetracing finger relative to the pattern may be controlled as desired byadjusting the speed ratio between the input shaft 521 and the outputshaft 523 of the drive 522 by means of handwheel 519. It is therebypossible to utilize a sinecosine cam suchas the cam 199 (Fig. of fixeddisplacement so that the sine-cosine voltages produced by thetransformers 195 and 196 are always of the same magnitude regardless ofthe feed rate employed. This system has a further advantage in that thethrow of the yokes 463 and 482 (Fig. of the pumps remains the same forall feed rates thereby eliminating inaccuracies in the operation of thetracer control system which would be introduced by attempting to operatethe pumps Very close to their positions of zero displacement in order toobtain low feed rates.

Throttling control circuit The tracer control mechanism hereinbeforedescribed is provided with means for reducing the feed rate of thecutter relative to the workpiece and of the tracing finger relative tothe pattern when abrupt changes in the pattern outline are sensed by thetracing finger 40 so as to provide time for the tracing finger to rotateand signal a change of direction to the table and cross-slide throughthe sine-cosine transformers. In this way, the feed rate of the machinetool will automatically be adjusted in the manner necessary to permitaccurate reproduction of abrupt corners occurring in the pattern ormaster being traced.

Referring to Fig. 10 of the drawings, the tube 311 which amplifies theerror signal produced by the transformer 174 in response to deviationsof the tracing finger from its position of normal displacement, hasconnected to its plate one end of a potentiometer winding 535 the otherend of which is connected to ground. The slider of this potentiometer isconnected to the grid of a phase inverter tube 536 the plate and cathodeof which are suitably coupled to the grids of a push-pull amplifier tube537. The plates of this tube are fed from the supply terminal 255through the center tap of the primary winding of a transformer 538. Thecenter tap of the secondary winding of the transformer 538 is maintainedat a predetermined potential with respect to ground by a voltage dividerincluding resistors 539 and 540. The plates of a full-wave rectifiertube 541 are connected to the end terminals of the secondary winding oftransformer 538 while the cathodes of the tube 541 are tied together andconnected to the center tap of the secondary winding through aresistance-capacitance filter network and a load resistor 542 connectedto a line 543 which is joined to the center tap.

When the machine tool is set for hand servo operation, the line 543 isconnected with the grid of a bias tube 544 through a pair of normallyclosed relay contacts 341-1 which are associated with a relay 341 (Fig.10). This relay also controls a pair of normally open contacts 341-2which are connected across the load resistor 542. When the relay 341 isenergized, the contacts 341-1 will open and the contacts 341-2 willclose thereby connecting the grid of bias tube 544 to the upper end ofload resistor 542 in place of the line 453.

The cathode of tube 54-4 is connected through a biasing resistor 547 toground and through a line 548 to the cathode of throttle tube 377, thegrid of which is main tained at predetermined potential by a voltagedivider comprised of resistors 549 and 550 connected between the supplyterminal 255 and ground. The screen grid of the throttle tube is held ata constant'potential by means of a voltage regulator tube 551 which isenergized from the supply terminal through a voltage dropping resistor552.

When the machine tool is set for automatic tracer control, the contacts3 41-1 will be open and the contacts 341-2 will be closed therebyconnecting the grid of bias tube 544 to the output of rectifier tube541. Under these conditions, when the tracing finger 40 is deflected dueto a change in direction in the pattern outline, the error signalproduced by the transformer 174 and amplified by tube 537 and rectifiedby tube 541 will cause a voltage drop to occur across the load resistor542 with the upper end of the resistor positive with respect to the lead543. The size of this voltage drop will be proportional to the magnitudeof the error signal. This will cause an in-' crease in current flowthrough the bias tube 544 and cause the cathode of this tube and alsothe cathode of throttle tube 377 to become more positive. This increasesthe negative bias on throttle tube 377 thereby reducing the amplitude ofthe 10,000 cycle energizing voltage delivered to the primary windings ofthe sinecosine differential transformers and 196 in proportion to themagnitude of the error signal. Hence, the output voltages of thetransformers will be correspondingly reduced thereby reducing thedisplacement of the pumps 453 and 454 which operate the table andcrossslide of the machine.

Machine controls Referring to Fig. 9, it will be seen that power isprovided for the control circuit of the tracing apparatus by thesecondary winding of a power transformer 562, the primary winding ofwhich is adapted to be energized from the power line. The lines 565 and566 which are connected to the secondary winding will thereby beenergized and cause the solenoid 567 of valve 107 (Fig. 2) to beenergized through a normally open limit switch 568, mounted in thetracing head, which is normally held closed by an adjusting screw 569(Fig. 3) mounted in the right-hand end of the lever 168. As previouslyexplained, when the solenoid valve 107 is energized, the line 106 (Fig.2) is connected to drain thereby permitting. the half nut 101 to engagethe feed screw 10% so as to place the tool head under hand servocontrol. However, in the event of overdeflection of the tracing finger40 to a point where damage to the machine might occur, the adjustmentscrew 569 will permit the contacts of switch 568 to open therebyde-energizing solenoid valve 107 and connecting line 106 to thehighpressure supply line 67 of the hydraulic system. This will removethe half nut 101 from the feed screw and allow spring 103 (Fig. 2) tomove the plunger of valve 72 upwardly thereby supplying fluid underpressure through line 86 to the upper end of cylinder 61 so as toelevate the tool head and lift the cutter and tracing finger away fromthe workpiece and pattern. After the overdefiected condition of thetracing finger has been eliminated, the switch 568 will again be closedto energize solenoid valve 107 and reengage the half nut 1&1 therebyenabling the head to be moved down under hand servo control.

Referring to Fig. 10 it will be seen that the coil of relay 341 isconnected in the plate circuit of a triode vacuum tube 571 whichcontrols the energization of relay 341. The grid of tube 571 isconnected by a resistor 572 to the plates of a full-wave rectifier tube573 and by a second resistor 574 to ground. The resistors 572 and 574form a load circuit for the tube 573, the cathodes of which areconnected to the end terminals of the secondary winding of transformer538.

When the tracing finger is hanging free, a high level error signal isproduced by the differential transformer 174 which is amplifier by thetube 537 and rectified by the tube 573 whose cathodes are connected toground through resistors 575 and 576. A negative voltage will thereby bedeveloped across the resistor 574 which Will apply a negative bias tothe grid of tube 571 and prevent energization of the coil of relay 341.However, as soon as the tracing finger is deflected toward its nullposition, the error signal will be diminished thereby reducing thenegative bias on the grid of tube 571 to a point where sufficientcurrent will be conducted by the tube to energize relay 341. This willcause contacts 341-3 of the relay to close thereby locking in the relaythrough a normally closed push button switch 50, mounted on the tracinghead 39 (Fig. 1), and the voltage dropping resistor 577. It will benoted that one of these contacts is connected to ground while the otheris connected to a junction 560 which in turn is connected to oneterminal of switch 50. The junction 560 is also connected to one end ofthe winding of relay 358 (Fig. 9). Hence, the contacts 341-3 will closea circuit through the coil of relay 358 (Fig. 9) to ground and energizethis relay. This will cause the previously mentioned contacts 358-2 and358-3 (Fig. 11) of this relay to open and the contacts 358-1 thereof toclose. At the same time, a further set of contacts 358-4 (Fig. 9)controlled by this relay will be closed thereby energizing the solenoid579 of a solenoid valve 580 (see also Fig. 2). When the valve 580 isenergized, fluid will be delivered under pressure through line 581behind the plunger 74 of the selector valve 73 so as to shift the valvefrom hand servo control position to tracer control position, the chamberat the end of plunger 75 being connected to drain through a line 582connected to a port on a hydraulic push button valve 583 having anoperating button 584 (see also Fig. l). The table and cross-slide willnow be placed under the control of the variable displacement pumps ofthe tracer control system and control of these elements by the handservovalves 7t) and 71 Will be disabled. The machine will continue tooperate under tracer control until switch i? is held depressed While thetracing finger is manually steered away from the pattern by grasping theknurled ring 131 (Fig. 3) and turning it forcibly away from the pattern.The finger will now hang free and cause a large error signal to beproduced which will bias the grid of tube 571 negative and de-energizerelay 341. This will cause contacts 341-3 (Fig. 9) to open therebydropping out relay 358. Contacts 358-4 will thus be opened tode-energize solenoid valve 580 and connect line 581 to drain. Contacts358-1 (Fig. 11) will be opened and the machine may now be steered bysimply turning the knurled ring 131 in the direction desired.

If the operator wishes to restore the machine to hand servo control, thehydraulic push button 584 is depressed so as to connect the line 582 tothe pressure line 67 and shift the selector valve 73 to the Handposition. It will be noted that whatever the condition of the machine,when the tracing finger is deflected toward its null position with theswitch 50 in its undepressed position, the relay 341 will pull in andcause the machine to be set for full automatic tracing.

To facilitate setting up the machine for tracer operation, it isdesirable to lock the tracing finger 40 in its vertical position asshown in Fig. 3 and for this purpose a knurled head 586 is provided onthe upper end of the threaded sleeve 186 to permit the sleeve to beturned downwardly until its lower end abuts against the upper edge oflever 168 and locks it against upward movement. Thiswill hold the fingeragainst displacement until the sleeve is backed 011 by reverse rotationthereof by the operator of the machine. To safeguard the mechanismagainst damage should the operator forget to return the sleeve 186 tothe position shown in Fig. 3 where the lever 168 is free to moveupwardly under the control of the finger to control operation ofthe'machine in the intended manner, a limit switch 564 is placed in thetracing head so that the normally closed contacts of the switch will beopened when the sleeve 186 is turned down to lock the finger. As shownin Fig. 5, the switch 564 is mounted on the body 171 immediately beneatha flange 587 formed on the upper end of sleeve 186. The operating buttonof the switch lies in contact with the bottom surface of the flange andwill be depressed thereby when the sleeve is screwed down into the blockso as to open the contacts of the switch. The switch 564 is preferablylocated in the control circuit of the pump driving motors 64 (Fig. 2)and 520 (Fig. 15) so as to disable the motors while the switch is openand thereby prevent operation of the machine while the tracing finger islocked. 7

Operation The tracer controlled machine tool heretofore describedoperates as follows:

The workpiece 28 and pattern 41 (Fig. 1) are mounted on the table 21 ofthe milling machine as shown after which the tracing finger 40 is soadjusted with relation to the cutter 27 as to occupy the same relativeposition with respect to the pattern 41 that the cutter occupies. withrespect to the workpiece 28, it being assumed that the workpiececorresponds generally to the shape of the pattern 41. To set the machineinto operation, the operator may feed the tracing finger 40 against thepattern by manipulation of handwheels 45 and 46 thereby causing thedifferential transformer 174 (Fig. 3) to approach its null position.This will decrease the bias on relay tube 571 (Fig. 10) and cause relay341 to pull in and close contacts 341-3 (see also Fig. 9) soas to lockin the relay and energize relay 358. The latter relay, when energized,closes contacts 358-4 and energizes solenoid valve 5% (Fig. 2) so as toshift selector valve 73 from Hand position to Tracer position. Asheretofore explained, this will cause the table and cross-slidecylinders 55 and 58, respectively, to be connected in a closed systemwith the variable displacement pumps 453 and 454 and render ineffectivethe control of the cylinders by hand servovalves 70 and 71. Energizationof the relay 358 also causes contacts 358-2 and 358-3 (Fig. 11) to open,and contacts 358-1 in the plate circuit of power amplifier tubes 351 and352 to close, thereby conditioning the rotation control circuits foroperation.

An alternative method of engaging the finger with the pattern is tomanually deflect the tracing finger so as to condition the machine forfull automatic tracing, and then release the finger with the switch 50depressed. This will cause the relays 341 and 358 to drop out, aspreviously explained, but will allow the selector valve 73 to remain inTracer position. The finger may now be steered into contact with theedge of the pattern by suitable manipulation of knurled ring 131. Assoon as the finger is deflected by the pattern, it will cause the relaysto pull in and thereby condition the machine for full automatic tracing.Y

Referring to the block diagram of the tracer control system shown inFig. 14, as herein indicated the templet 41 acts on the tracer finger 40to deflect it from its vertical or free position as shown in Fig. 3. Thetracing finger controls the rotation transformer or pickup 174 to whichis fed an energizing voltage produced by the oscillator and filter 284.As heretofore explained, this voltage is applied to the primary windingof the transformer and anerror signal is produced on the output terminalof the secondary windings whenever the tracing finger is overdeflectedor underdeflected from its normal or null position. The error signal isamplified by tube 311 (Fig. 10) and push-pull amplifier tube 320 (Fig.11) after which it is passed to the discriminating circuit includingtube 330 for the purpose of ascertaining the phase of the error.

signal. .The discriminated signal is then rectified by tube

